Fully filled plaster sheathed telecommunication cables



C. D. FORBER Aug. 25., 1970 FULLY FILLED PLASTIC SHEATHEDTELECOMMUNICATION CABLES Filed March 21, 1968 PETROLEUM 8-P0L YETHYL ENELOW DENSITY POL YE TH YL ENE POLYVl/VYL D/ETHYLENE COPOLYMER 5 HI/t.

CELLULAR POLYETHYLENE United States Patent Office 3,525,798 PatentedAug. 25, 1970 U.S. Cl. 174-26 9 Claims ABSTRACT OF THE DISCLOSURE In afully filled plastic sheathed multi-conductor telecommunication cablethere is provided between the conductors and the sheath a separatinglayer which will serve both as a heat barrier and a barrier to thepassage through the sheath of the filling material and which will bondto the sheath at or below the temperature at which the sheath isextruded on the core.

This invention relates to telecommunication cables of the kindcomprising a multiplicity of plastic insulated conductors enclosedwithin a waterproof sheath and, filling the interstices between theinsulated conductors and between them and the waterproof sheath from endto end of the cable length, a water-impervious medium which will notdrain under the influence of gravity or such hydrostatic pressure as mayarise in the event of damage to the cable sheath but which will permitrelative sliding movement of the plastic insulated conductors over oneanother during such bending of the cable as occurs during manufactureand installation of the cable.

The non-draining water-impermeable medium generally preferred ispetroleum jelly. The material used for the sheath is generallypolyethylene. However as polyethylene is pervious to petroleum jelly thepossibility exists, especially when such fully-filled, plastic sheathedtelecommunication cables are laid in the vicinity of heavy current powercables, of filling material migrating into and under certain conditionsthrough the polyethylene sheath, thus creating an incompletely filledcable along which moisture may travel.

By the present invention there is provided an improved form of fullyfilled plastic sheathed telecommunication cable in which the risk ofmigration of the filling medium through the cable sheath issubstantially eliminated.

The improved form of cable comprises a core comprising a multiplicity ofplastic insulated conductors enclosed within a sheath of plasticmaterial pervious to petroleum jelly and like mixtures ofmicrocrystalline petroleum waxes and oils at certain ambienttemperatures, the interstices between the individual conductors of thecore and between the core and the sheath being filled with petroleumjelly or a like mixture of microcrystalline petroleum wax and oil,wherein there is present between the core and the sheath a separatinglayer which will serve both as a heat barrier and a barrier to thepassage of the material with which the interstices are filled and whichwill bond to the sheath at or below the temperature at which the sheathis extruded on the core.

Where the cable sheath is of polyethylene the separating layer mayconsist of a layer or coating of polyvinyl diethylene copolymer on acarrier layer which will bond, or which carries a layer which will bond,to polyethylene at temperatures of about 200 C., which temperatures arethe temperatures at which a polyethylene sheath is generally extruded ona cable core.

The separating layer is preferably a laminate consisting of a carrierlayer of cellulose acetate carrying on one face a coating of polyvinyldiethylene copolymer and on the other face a coating of a low densitypolyethylene. The separating layer is preferably formed bylongitudinally applying to, or helically lapping on, the cable core atape of the laminate in such a way that the polyethylene layer is on theoutside and contiguous margins of the tape overlap one another to form acomplete envelope on to which the polyethylene sheath is extrudedpreferably at a temperature and under conditions which ensure that theexposed parts of the surface of the polyethylene layer become bonded tothe polyethylene sheath.

Preferably the coating of polyvinyl diethylene copolymer on one face ofthe laminate itself carries an outer coating of a low densitypolyethylene, thereby providing a laminate having an outer coating ofpolyethylene on each of its faces. Use of a tape of the laminate of thislatter form as the separating layer ensures that a bond is obtainedbetween the overlapping margins of the tape when the polyethylene sheathis extruded on the core. Moreover, since the tape has a polyethylenecoating on each of its faces, the tape can be applied to the cable corewith either of its polyethylene layers on the outside and the necessity,present when employing a tape of laminate carrying on one face only apolyethylene coating of detecting which surface of the tape has thepolyethylene coating is eliminated.

In both cases the tape of the laminate also serves as a thermal barrierenclosing the cable core and serving to prevent overheating of theconductor insulation during the operation of extruding the sheath.

The invention will now be more fully described, by way of example, withreference to the accompanying drawing which is a fragmentalcross-sectional view, drawn to an enlarged scale, of a preferred form oftelecommunication cable constructed according to the present invention.

The cable comprises a multiplicity of copper conductors 1 each having adielectric 2 of cellular polyethylene. Helically lapped about themultiplicity of conductors in such a way that its contiguous marginsoverlap one another to form a complete separating envelope 3 is a tapeof a laminate consisting of a carrier layer 4 of cellulose acetatecarrying on one face a coating 5 of polyvinyl diethylene copolymer andcarrying on its other face and on the polyvinyl diethylene copolymercoating 5, coatings 6 of a low density polyethylene. A polyethylenesheath 8 is extruded on and bonded to the outer polyethylene coating 6of the separating envelope 3, the overlapping contiguous margins of thetape also being bonded together. The interstices between the individualcellular polyethylene insulated conductors 1 and between them and theseparating envelope 3 are filled throughout the length of the cable witha water-impermeable medium consisting of petroleum jelly 7. If required,the cable may be provided with armouring (not shown) comprisinggalvanized steel wires laid helically over the sheathed cable andprotected against corrosion by an extruded oversheath of polyvinylchloride.

In some cases it may be necessary to lay telecommunication cables, suchas pilot and telephone cables, underground alongside heavy current powercables designed for a continuous maximum conductor temperature of C. Insuch cases there is a tendency for moisture in the soil to be drivenaway from the vicinityof the feeder cables. This in itself may beconducive to the bleeding of petroleum jelly or other similar fillingmedium from the neighbouring fully filled pilot and telephone cable ifof normal construction. This risk is avoided by constructing the pilotand telephone cable or cables in accordance with the invention.

What I claim is:

1. A telecommunication cable comprising a multiplicity of plasticinsulated conductors forming a core enclosed within a sheath of plasticmaterial pervious to petroleum jelly and like mixtures ofmicrocrystalline petroleum waxes and oils at certain ambienttemperatures, the interstices between the individual conductors of thecore and between the core and the sheath being filled with one of saidmixtures of microcrystalline petroleum waxes and oils, wherein there ispresent between the core and the sheath a separating layer which willserve both as a heat barrier and a barrier to the passage of thematerial with which the interstices are filled and which will bond tothe sheath at or below the temperature at which the sheath is extrudedon the core.

2. A telecommunication cable as claimed in claim 1, wherein theseparating layer consists of a layer of polyvinyl diethylenc copolymeron a carrier layer which will bond to the sheath at or below thetemperature at which the sheath is extruded on the core.

3. A telecommunication cable as claimed in claim 2, in which the sheathis of polyethylene, wherein the carrier layer of the separating layerwill bond to polyethylene at temperatures of about 200 C.

4. A telecommunication cable as claimed in claim 1, wherein theseparating layer consists of a layer of polyvinyl diethylene copolymeron a carrier layer which carries a layer which will bond to the sheathat or below the temperature at which the sheath is extruded on the core.

5. A telecommunication cable as claimed in claim 4, in which the sheathis of polyethylene, wherein the carrier layer of the separating layercarries a layer which will bond to polyethylene at temperatures of about200 C.

6. A telecommunication cable comprising a multiplicity of plasticsinsulated conductors forming a core enclosed within a sheath ofpolyethylene pervious to petroleum jelly and like mixtures ofmicrocrystalline petroleum waxes and oils at certain ambienttemperatures, the interstices between the individual conductors of thecore and between the core and the sheath being filled with petroleumjelly, wherein there is present between the core and the sheath aseparating layer comprising a laminate consisting of a carrier layer ofcellulose acetate carrying on its inner face a coating of polyvinyldiethylene copolymer and on its outer face a coating of a low densitypolyethylene which will bond to the polyethylene sheath at or below thetemperature at which the polyethylene sheath is extruded on the core,which separating layer will serve both as a heat barrier and a barrierto the passage of the material with which the interstices are filled.

7. A telecommunication cable as claimed in claim 6, wherein theseparating layer is formed by applying to the cable core a tape of thelaminate in such a way that the polyethylene layer'is on the outside andcontiguous margins of the tape overlap one another to form a completeenvelope on to which the polyethylene sheath is extruded.

8. A telecommunication cable comprising a multiplicity of plasticinsulated conductors forming a core enclosed within a sheath ofpolyethylene pervious to petroleum jelly and like mixtures ofmicrocrystalline petroleum waxes and oils at certain ambienttemperatures, the interstices between the individual conductors of thecore and between the core and the sheath being filled with petroleumjelly, wherein there is present between the core and the sheath aseparating layer comprising a laminate consisting of a carrier layer ofcellulose acetate carrying on one face a coating of polyvinyl diethylenecopolymer and carrying on its other face and on the coating of polyvinyldiethylene copolymer coatings of a low density polyethylene, theoutermost of which polyethylene coatings will bond to the polyethylenesheath at or below the temperature at which the polyethylene sheath isextruded on the core, which separating layer will serve both as a heatbarrier and a barrier to the passage of the material with which theinterstices are filled.

9. A telecommunication cable as claimed in claim 8, wherein theseparating layer is formed by applying to the cable core a tape of thelaminate in such a way that contiguous margins of the tape overlap oneanother to form a complete envelope on to which the polyethylene sheathis extruded.

References Cited UNITED STATES PATENTS 3,445,324 5/1969 Curler et al.161-165 2,345,229 3/1944 Barmack 15652 X 3,427,394 2/ 1969 McKean 17425X 3,188,265 6/1965 Charbonneau et al. 161188 2,860,801 11/1958 Nielsen117 -94 X 2,968,576 1/1961 Keller et al. 117-47 3,344,228 9/1967Woodland et al. 174-107 3,098,113 7/1963 Brierley 174-26 FOREIGN PATENTS776,174 6/ 1957 Great Britain.

LARAMIE E. ASKIN, Primary Examiner A. T. GRIMLEY, Assistant ExaminerU.S. Cl. X.R. 174--110, 120

